In a wireless communication system, a base station refers to a device providing services for a terminal and communicating with the terminal through an uplink and a downlink, wherein the DownLink (DL), which is also called a forward link, refers to a direction from the base station to the terminal, and the UpLink (UL), which is also called a reverse link, refers to a direction from the terminal to the base station. Multiple terminals can send data synchronously to a base station through an uplink or receives is data synchronously from a base station through a downlink.
In a mobile network, the quality of wireless coverage is the key for a terminal to enjoy high-speed data service as well as voice and video service. At present, in order to achieve seamless coverage of a wireless network, the main efforts should focus on realizing coverage over indoor areas and hotspot areas. In order to address the coverage problem above, there have been currently provided two main solutions, in one of which the number and the density of Macro Base Stations (Macro BS) are increased, wherein a Macro BS is also called a Macro Cell, and in another of which a small base station with lower transmit power, such as a Femto Base Station (Femto BS or Femto Cell), a Micro Base Station (Micro BS or Micro Cell) and a Pico Base Station (Pico BS or Pico Cell), is installed indoor, wherein the Femto BS is also called a personal BS.
According to Shannon principle, the current adoption of conventional Macro BSs is approximate to a capacity limit of the use of a frequency spectrum, any increase in the high-power Macro BSs will only result in more radiation pollution but no contribution to indoor coverage, whereas, the use of a small base station such as a Femto BS or a Pico BS can not only perfectly realize coverage over indoor areas and hotspot areas but also increase system capacity significantly on the basis of existing frequency spectrum resources.
A Femto BS can provide services for all users or only for a group of specific authorized users. For the reasons such as signal fading, interference or a higher requirement on Quality of Service (QoS), a Mobile Station (MS) may transfer from an air interface of a base station (called a serving base station) to an air interface of another base station (called a target base station), this process is called switching. If there exists a Macro BS as well as a Femto BS and a Pico BS in a system, a terminal may need to be switched among the Micro BS, the Femto BS and the Pico BS. There have been currently provided two main switching methods: method 1: a Macro BS broadcasts information of a neighboring cell list (the information indicates some basic information related to an available BS nearby the Macro BS), and an MS searches for a BS recorded in the neighboring cell list according to the information of the neighboring cell list and then performs switching, this switching method will cause a high signaling overhead, and additionally, the MS may find, according to the information of the neighboring cell list, a great number of Femto BSs and Pico BSs which may be unsuitable for the MS; and method 2: an MS automatically searches for a Femto BS or Pico BS suitable for switching, as there may be numerous Pico BSs and Macro BSs which may work at different carrier frequencies, this method will increase the searching complexity of the MS and is hardly conducive to power saving.